Au Nanorings/TiO<sub>2</sub> NPs@MXene-Based Metasurfaces\nwith a Magnetic Mirror-Modulated ECL Strategy for Extracellular Vesicle\nDetection

A metasurface as an artificial electromagnetic structure\ncan concentrate\noptical energy into nanometric volumes to strongly enhance the light–matter\ninteraction, which has been becoming a powerful platform for optical\nsensing, nonlinear effects, and quantum optics. Herein, we developed\na novel hybrid plasmonic-dielectric metasurface consisting of Au nanorings\n(Au NRs) and TiO<sub>2</sub> nanoparticles derived from MXene (TiO<sub>2</sub> NPs@MXene). The hybrid metasurface simultaneously benefited\nfrom the high near-field enhancement effect of plasmonic materials\nand the low loss of dielectric materials. Furthermore, the optical\nmodulation efficiency of the hybrid metasurface can be regulated by\na magnetic mirror configuration. The magnetic mirror acted like a\nmirror, confining the electrons to a limited region and increasing\nthe density of the surface plasmon. Moreover, the electrochemiluminescence\n(ECL) of the Cu<sub>2</sub>BDC metal–organic framework (Cu<sub>2</sub>BDC-MOF) served as a light source for the Au NRs/TiO<sub>2</sub> NPs@MXene metasurface. Due to the exceptional light manipulation\ncapability of the hybrid metasurface and the coordination of the magnetic\nmirror, the isotropic ECL signal can be dynamically amplified and\nconverted into polarized emission. Finally, a metasurface-regulated\nECL (MECL)-based biosensor with a dual-positive membrane protein recognition\nstrategy was developed for the accurate identification of gastric\ncancer-derived extracellular vesicles. The novel MECL research opened\nup a new route in the realization of dynamically tunable metasurfaces\nfor optical sensing and novel nanophotonic devices.